A subclient is a logical entity that contains the user accounts that need to be backed up. A default subclient is automatically created under the first instance and any subsequent instances that you create.
If you have different backup requirements for some Google user accounts, you can create user-defined subclients to manage these different requirements. Use these subclients to manually discover user accounts, and then assign each user account to the subclient that meets its backup requirements. For information on creating a user-defined subclient, see Creating Subclients to Back Up Specific User Accounts.
Manually discover all your Google user accounts using the default subclient. You can then assign all the user accounts to the default subclient, and run a single backup operation to back up all the user accounts. For information on manually discovering user accounts from a subclient, see Manually Discovering User Accounts.
Use the user-defined subclients to auto discover user accounts. To auto discover the user accounts, you can either provide regular expressions to match the name of the user accounts, or you can provide a Google sub organization name that contains all the user accounts that you want to discover. You can then run a backup operation on this subclient to back up the user accounts. For information on auto discovery of user accounts from a subclient, see Auto Discover User Accounts.
Note
Any user account that is not assigned to a subclient gets automatically assigned to the default subclient. To disable this feature, from the Subclient Properties of default dialog box, on the Auto-discovery tab, clear the Automatically add new mailboxes that do not qualify for membership in any of the subclients check box.